Attention has been focused on a technique for forming a transistor using a semiconductor thin film (also referred to as a thin film transistor (TFT)). Such a transistor is applied to a wide range of electronic devices such as integrated circuits (ICs) or image display devices. A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor. As another material, an oxide semiconductor has been attracting attention.
For example, a transistor including an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) as a channel formation region is disclosed (see Patent Document 1).
Further, it is known that oxygen is released from an oxide semiconductor in a manufacturing process to form oxygen vacancies (see Patent Document 2).